A “stamping wheel for burnishing shaft parts, particularly the axle journal and wheelset fail-safes” is known from the German patent document no. 808 197. The working surface of the stamping wheel consists of one cylinder, to which, on the one hand, a large rounding for the large corner groove of the axle journal and, on the other hand, a small rounding for the small corner groove on the axle collar are connected. The axle for the stamping wheel is supposed to adopt a skewed position to the axle of the axle journal during the burnishing procedure and, when pressed into the axle journal at one position, create a long, drop-shaped imprint on the surface of the axle journal.
At the time the above-mentioned German patent was registered, deep rolling was called “burnishing”. A company brochure of the applicant from 1954 then shows a machine which can be used to deep roll the two axle journals on a wheelset from their respective outer ends. Only the axle journals of finished wheelsets were machined respectively. To do this, two pairs of work rollers were used which were each meshed simultaneously onto the axle journals for the wheelset. In those days, the wheelset was driven via a transmission belt, which was looped around one of the two wheel discs for the wheelset. With the known machine, the axle journals for the wheelset were rigidified to such an extent that, along with having an improved surface quality, they also had simultaneous higher strength, whereby hot axle boxes were able to be prevented on the one hand and axle journal breakage on the other. The known deep rolling operation therefore meant that internal stresses were introduced into the surface of the axle journal which led either to no cracks being produced or cracks that were already produced being able to be brought to a stop. The outcome was that an increase in the service life of the wheelset was achieved.
As well as the treatment of the axle journal, a “device for burnishing cylindrical workpieces like shaft parts” is already known from the German patent document no. 843 922. The known device features one or more work rollers, whereby each work roller is mounted in a pivoting carrier whose swivel axis runs both vertically to the infeed motion of the work roller and vertically, or nearly vertically, to the workpiece axis. The known device was supposed to be used mainly for machining cylindrical shafts, which does not rule out that it could be used for deep rolling wheelset shafts, too.
Damage to the wheelset shafts of railway high-speed vehicles which has recently occurred has led to particular attention being paid towards the finishing of the wheelset shafts. In doing so, the formation of cracks in particular is to be counteracted.
On the basis of the knowledge that by introducing residual compressive stresses into the surface of crankshafts, the formation of cracks can be prevented or cracks that have already occurred can be brought to a stop, the task of this invention is now to propose a modern machine which can be used to deep roll the wheelset shafts of wheelsets for railway vehicles before the wheel discs are fitted. As is well known, a wheelset shaft is characterised in that it features several adjacent lengthwise sections (hereinafter referred to as axle zones) with different diameters.
In a machine tool of the type specified, this invention means the task is solved by having tools that comprise more than two pairs of work rollers, of which each pair is intended for deep rolling at least one axle zone on the wheelset shaft. In a favoured variant, the tools comprise three pairs of work rollers.
Here, it is intended that the first pair of work rollers be used to deep roll the axle journals and transition piece, a second pair of work rollers to deep roll the press seating for one wheel disc and a third pair of work rollers to deep roll the stub shaft from the press seating at least up to the longitudinal centre of the wheelset shaft.
Ideally, the work rollers forming the first and second pair are each arranged together in one housing. This housing can be moved in the y-direction of the machine tool. Owing to the movability in the y-direction, the work rollers for the first and second pair of work rollers are meshed one after the other. At the same time, the housing can be pivoted around a B-axis of the machine tool. This movability makes it possible to machine the transitions between the individual axle zones of the wheelset shaft. As is well known, the transitions are arranged as corner grooves.
The first and the second pair of work rollers are at a specified fixed axial distance away from the third pair of work rollers in the z-direction of the machine tool. All three pairs of work rollers are ultimately arranged together on one slide. The common slide can be moved in the z-direction of the machine tool, i.e. in the feed direction. Two slides in total are provided on the machine tool, each of which is designated to the respective end of the wheelset shaft. When the axle zones are deep rolled, the two slides move towards each other at feed rate.
Ultimately, the crankshaft deep rolling tools can also be adjusted in the x-direction. A servo motor is used to feed in two work rollers, each forming one pair, in the direction of the wheelset shaft at the same time. Notably, all three pairs of work rollers are moved at the same time. The deep rolling force is also set via the infeed in the x-direction.